Could I be pregnant?

hello doctor i have a concern an question, on april 24th 2010 i had unprotected sex for the first time in 8 months! a couple days after i started experiencing light cramping til today im still experiencing cramping sharp pains on my left an right side and under my belly button it sometimes feels sharp in my vaginal area, it feels sort of fuzzy bubbly moving cramps, my lower back hurts from time to time i get sharp breast pains an head aches, im not due for my period til may 19. i do have certain days where im nauseous i took a pregnancy test it was negative can u tell me what can it be?